1. Field of the Invention
This invention relates to hydraulic drive systems and particularly such systems as are used in raising and lowering platforms, cages, and the like. More particularly, it relates to a hydraulic drive system in which a plurality of cylinder/piston assemblies are cascaded together so as to decrease the total length occupied by the system when it is in retracted, or in the case of an elevator, lowered position.
2. Description of the Prior Art
When two or more cylinder/piston elevator arrangements or systems are cascaded so as to minimize the length of the system when in retracted or lowered position, the systems must be laterally displaced with respect to each other in order to achieve the shortening effect desired. This lateral displacement produces non-aligned forces on the system which result in torque about a horizontal axis which must be accommodated one way or another.
One way of doing this is to balance the pistons so that there are, for example, two cylinder/piston systems side-by-side on opposite sides of a central axis. This has the disadvantage of requiring an extra cylinder/piston assembly.
Unless such balance is achieved, it is necessary to make each component sufficiently large and strong that it can withstand the bending moment created by the offset pistons. Strengthening the cylinder/piston structure is not only expensive, since precisely machined parts must be accommodated, but it also subjects these parts to lateral forces which make sealing between piston and cylinder more difficult.